Beta Titanium Research Articles

Evolution of microstructure and mechanical properties of vacuum electron beam welded joints in a near beta titanium alloy: Influence of heat treatment

Herein, the two plates of a near beta titanium alloy (Ti55531) with a thickness of 60 mm were welded by vacuum electron beam welding, and full penetration welded joints were obtained. The results show that the welded joint can be divided into weld bond, heat affected zone and base metal. Microstructures of weld bond and heat affected zone are composed of coarse β grains and fine α phases distributed at the β grain boundaries and in the β grains, and the β grains in weld bond are coarser than those in heat affected zone. The solution treatment can reduce the microhardness and improve the impact toughness of different zones of the joint. The tensile strength of the welded joint can be improve to 1129 MPa by solution and aging treatment. The influence of heat treatment on microstructures and mechanical properties of these welded joints were discussed in detailed.

Effect of Molybdenum Content on Microstructure and Mechanical Properties of Ti-Mo-Fe Alloys by Powder Metallurgy

Titanium has many limitations in coverage and frequency of application due to its expensive alloying elements and complex manufacturing process. The biocompatible Ti-Mo-Fe ternary beta titanium alloys were designed by replacing high-cost beta-stabilizer elements (V, Nb, Zr, etc.) with low-cost Mo and Fe elements. In addition, it was attempted to obtain a low-cost, high-strength beta-titanium alloy with 800 MPa or more by applying the powder metallurgy process technology to the Ti-Mo-Fe alloy system. The added Mo element has the effect of reducing the elastic modulus of the titanium alloy without reducing its strength. In this study, Ti-Mo-Fe alloys designed with different Mo contents were fabricated using a powder metallurgy process and analyzed in connection with microstructural properties, phase changes, and mechanical properties. As Mo contents are increased, the α-lath thickness of Widmanstätten decreases and the size of prior β grain decreases. It was confirmed that the hardness and tensile strength were excellent and were compared with the ingot material of the same alloy system.

A study on tensile flow and strain hardening behaviour of β-Titanium at elevated temperatures

In this paper, the tensile flow and work hardening behaviour of Beta titanium alloy was examined over a wide temperature range of 28 to 500°C. The work hardening of the material was modelled using different empirical relations such as Swift, Voce and Ludwigsen and the prediction accuracy of these models were compared with different statistical parameters. The hardening rate of the material was analysed with K-M analysis. The fracture behaviour of the tensile samples was studied using SEM results. The yield strength and ultimate tensile strength of the material was found to be decreased from room temperature to 200°C followed by a gradual increase with increase in temperature. Uniformly distributed serrations were observed in the entire plastic region of the flow curve in the temperature range of 200– 400°C. This serrated behaviour could be due to the manifestation of dynamic strain aging in this temperature range. The Voce hardening model was identified as a best hardening model to describe the material hardening. SEM results revealed the ductile mode of fracture at all temperature with large number of dimples in fractographs.

Increasing the yield strength while preserving strain hardenability and ductility in a beta titanium alloy exhibiting transformation induced plasticity (TRIP)

The commercial β-Ti alloy, Ti-10V-2Fe-3Al; primarily used with an α+β microstructure, exhibits a high yield strength but with poor strain-hardenability and limited ductility. This paper focuses on the interplay between stress-induced martensite (α”) in this alloy, introduced via prior cold-rolling (5,10, 20, and 30%) and additional martensite (α”) forming during subsequent tensile loading, leading to a simple way to substantially increase the yield strength while enhancing the high strain hardenability (via TRIP) and maintaining the uniform tensile ductility. The results indicate that the YS in this alloy can be substantially tuned from 400 to 1800 MPa, via cold-rolling. Among the various conditions that were analyzed, the 5% cold-rolled condition offered the best combination of YS (∼900 MPa), ductility (8%) and the strain hardenability. The stress-induced α” formation during tensile loading is essential for maintaining the high strain-hardening and, consequently the uniform tensile ductility in this alloy.

High-temperature deformation behavior and recrystallization mechanism of a near beta titanium alloy Ti-55511 in β phase region

Isothermal compression tests, electron backscatter diffraction (EBSD) observations and quantitative analysis were performed to investigate high-temperature deformation behavior and recrystallization mechanism of Ti-55511 alloy in β phase region. The stress-strain curves, calculated activation energy and microstructure characterization show that dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main soften mechanisms. DRX becomes more significant with decreasing strain rate and increasing deformation temperature and true strain. Recrystallization grains are identified by calculated grain orientation spread (GOS). It is found that quantitative microstructural characteristics, such as DRX volume fraction and DRX grain size, are strongly dependent on process parameters. The discontinuous dynamic recrystallization (DDRX) by grain boundaries bulging and continuous dynamic recrystallization (CDRX) by progressive sub-grains rotation are observed in the deformed microstructure of Ti55511 alloy. The flow softening rate and kinetics exponent of DDRX are higher than those of CDRX. With increasing deformation temperature, DRX mechanism has transformed from DDRX to CDRX, resulting in the unexpected decrease of DRX kinetics exponent nD and flow softening rate. The ηbcc fiber, εbcc fiber and ξbcc fiber are the dominant texture component in deformed Ti–55511 alloy. The weakening of the deformation texture is accompanied by the occurrence of DRX, which can be attributed to the random orientation distribution of DRX grains.

Static Recrystallization Behavior and Texture Evolution during Annealing in a Cold Rolling Beta Titanium Alloy Sheet

In this study, the cold rolling microstructure and static recrystallization mechanism of the high strength titanium alloy Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe were systematically investigated. Results show that the cold rolling microstructure is mainly composed of the elongated deformed β grains containing micro-shear bands. After annealing at 815 °C for 2 min, the fine SRXed grains are observed, mainly concentrated in the micro-shear band, the grain boundary and the interior of the deformed grain. The sub-grain structure obtained by static recovery inside the deformed grain produces continuous SRX during the annealing treatment. Meanwhile, geometric and discontinued SRXed grains are also observed in the large deformed β grain and at the trigeminal grain boundaries, respectively. Many ultra-fine grains appear inside the micro-shear band, exhibiting a phenomenon of the micro-shear band assisting SRX. With the increase in the annealing holding time, the elongated β grains are significantly refined and the degree of recrystallization is continuously improved. In addition, the recrystallization behavior also results in a significant change in the fiber texture. With the extension of the annealing holding time, the rolling texture type evolves gradually, with the {111} <112> γ-fiber texture to weak α-fiber, γ-fiber, and Goss-fiber.

Grain size-dependent tensile behaviour in a metastable beta titanium alloy

The present study investigates the effect of beta grain size on the stability of the beta phase in terms of trigger stress and the resultant mechanical properties of metastable beta titanium alloy. The trigger stress has a complex U-shaped relation concerning the beta grain size, which could be due to alternant mechanisms from interface friction and elastic energy. Nevertheless, the residual stress/strain could affect the trigger stress in the small grain size scale. More interestingly, dominant deformation modes are altered by a change of grain size with predominant stress-induced martensite (SIM) at small grain size and prime dislocation at large grain size, leading to grain size-dependent tensile behaviour of a metastable beta titanium alloy.

Orthodontic Management of Severe Dentoalveolar Collapse with Miniscrew-Assisted TMA Cantilever Springs and Bite Blocks

Introduction: Management of mutilated cases is challenging, and adult patients often require orthodontic correction of occlusion before prosthetic replacement of missing teeth. Objective: To highlight the novel, simple, hygienic, and efficient miniscrew-supported Beta titanium molybdenum alloy (TMA) cantilever spring for uprighting severe mesially tipped molars for interdisciplinary treatment. Diagnosis and Treatment: A 23-year-old male patient presented with skeletal Class I relation, average growth pattern, Class II Division 1 malocclusion with dentoalveolar collapse, crowding, multiple missing, supraerupted teeth, and severe mesially tipped mandibular third molars. MBT appliance with 0.022˝ slot was used to achieve the objectives. 38 and 48 were uprighted and protracted with miniscrew implant-supported TMA cantilever springs to substitute 37 and 47. Mild intrusion of maxillary posterior teeth was done with acrylic bite blocks and transpalatal arch (TPA), followed by prosthetic replacement of missing teeth. Results: The patient had a consonant smile arc and a pleasing soft tissue profile. 38 and 48 were uprighted and protracted with good vertical control, and the mesial pockets were eliminated. 17 and 27 were intruded, and group function occlusion was established. Class I canine relationship, normal overjet, and overbite were achieved. Conclusion: Miniscrew supported TMA cantilevers are efficient for uprighting of severely tipped 38 and 48 without extrusion, unlike the conventional mechanics. 18, 28, 38 and 48 with good root forms can be protracted and substituted as 17, 27, 37 and 47 respectively to minimize or eliminate prosthetic rehabilitation.

A review of the metastable omega phase in beta titanium alloys: the phase transformation mechanisms and its effect on mechanical properties

ABSTRACT Since its discovery in 1954, the omega (ω) phase in titanium and its alloys has attracted substantial attention from researchers. The β-to-ω and ω-to-α phase transformations are central to β-titanium alloy design, but the transformation mechanisms have been a subject of debate. With new generations of aberration-corrected transmission electron microscopy and atom probe tomography, both the spatial resolution and compositional sensitivity of phase transformation analysis have been rapidly improving. This review provides a detailed assessment of the new understanding gained and related debates in this field enabled by advanced characterization methods. Specifically, new insights into the possibility of a coupled diffusional-displacive component in the β-to-ω transformation and key nucleation driving forces for the ω-assisted α phase formation are discussed. Additionally, the influence of ω phase on the mechanical properties of β-titanium alloys is also reviewed. Finally, a perspective on open questions and future direction for research is discussed.

Initiation and propagation of small fatigue crack in beta titanium alloy observed through synchrotron radiation multiscale computed tomography

Synchrotron radiation computed tomography is an emerging nondestructive method for fracture analysis in materials. Herein, the in situ small-crack growth of a beta titanium alloy, Ti–22V–4Al, was monitored by a combination of microtomography (micro-CT) and nanotomography (nano-CT). The 3D characteristics of small cracks and the corresponding stress intensity factor range (ΔK) were obtained by micro-CT; the cracks initiated at ∼10% fatigue life. In the low-ΔK regime, the scatter of the crack aspect ratio and the deviation in the crack propagation rate were significant; however, they decreased with increasing ΔK, reflecting the microstructural effect on small-crack propagation. The microstructure of the beta titanium alloy was successfully visualized by nano-CT. Consequently, the crack-surrounding-microstructure interactions evidenced that the fatigue cracks initiated from the center of the beta grain wherein the alpha-phase was less precipitated.

Strain hardening behavior of friction welded beta titanium alloy Titan 1023 used for aeronautical applications

The experimental true stress – true strain data has been evaluated for the solution treated and aged beta titanium alloy Titan 1023 in comparison with the solid state welded samples. 14 mm diameter rods extracted out of Titan 1023 rolled bars were welded employing rotary friction welding with optimized parameters. Strain hardening parameters for samples in solution treated, aged condition and welded samples were determined using Holloman equation with the data obtained by carrying out tensile testing at ambient temperatures employing a strain rate of 3x10−4S−1. Strain hardening rate in terms of Crussard-Jaoul (C-J) plots of the alloy in all pre and post treated conditions were elucidated. Work hardening capacity of the alloy in STA and welded conditions were determined and presented. The effect of resultant microstructures on the strain hardening behavior is discussed in the current study.

Development of a novel metastable beta titanium alloy with ultrahigh yield strength and good ductility based on laser power bed fusion

Metastable β titanium alloys are known for excellent ductility and corrosion resistance but relatively low yield strength (YS) which restricts their application. In this study, a novel high strength metastable β titanium alloy, Ti-6Mo-5.5Cr-1Co-0.1C (wt%) was developed based on laser powder bed fusion ( L -PBF). It is shown that the as-fabricated material was dominated by mixed columnar and equiaxed β grains decorated by numerous fine TiC flakes. The precipitates were interconnected to each other and connected to grain boundaries (GBs) by dislocations. Solution treatment at 850 °C led to dissolution of intra-granular TiC and diffusion of C to GBs through dislocation pipes, which created vast carbide-free β grain interior areas that are good for deformation and promoted formation of bulk and polygonal TiC along GBs. The GB TiC particles acted as effective O getter of the matrix, which together with significant ω precipitation helped stabilize the β matrix. As a result, β → α′′ phase transformation and mechanical twinning have been suppressed. The samples deformed mainly through dislocation slip and ω → β reverse phase transformation. Ultrahigh YS and decent ductility have thus been achieved in the newly developed metastable β titanium alloy. The current work paves the way for developing high performance metastable β titanium alloys through additive manufacturing.

Unravelling the competitive effect of microstructural features on the fracture toughness and tensile properties of near beta titanium alloys

The competitive effect of microstructural features including primary α (αp), secondary α (αs), grain boundary α (αGB) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes. The relative effect of β grain size and STA (solution treatment and ageing) processing parameters on mechanical properties were quantitatively explored by the application of Taguchi method. These results were further explained via correlating microstructure with the fracture toughness and tensile properties. It was found that large numbers of fine αs precipitates and continuous αGB played greater roles than other features, resulting in a high strength and very low ductility (<2%) of STA process samples. The β grain size had a negative correlation with fracture toughness. In the samples prepared by BASCA (β anneal slow cooling and ageing) process, improved ductility and fracture toughness were obtained due to a lower density of αs precipitates, a basket-weave structure and zigzag morphology of αGB. For this heat treatment, an increase in prior β grain size had an observable positive effect on fracture toughness. The contradictory effect of β grain size on fracture toughness found in literature was for the first time explained. It was shown that the microstructure obtained from different processes after β solution has complex effect on mechanical properties. This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties. A novel table was proposed to quasi-quantitatively unravel these competitive effects.

Load Deflection Properties of Small Diameter Titanium-Niobium-Tantalum-Zirconium Archwire(An In Vitro Study)

Objectives: This study aimed to evaluate the load deflection properties of new niobium-based beta titanium archwire (Gummetal) in comparison with superelasticnickel titanium (SE-NiTi) and copper NiTinickel titanium (Cu-NiTi) archwires. Methods and Material: Gummetal, superelasticNiTiand copper NiTiarchwire segments of 0.014-inch diameter were examined by three point bending test, using Instron testing machine with 10 Newton (N) load cell. Wire segments were tested at 2 and 4 mmdeflections, and at a temperature of 37±1ᵒC. Oneway analysis of variancewas used to compare the means of the groups at a significance of p ˂ 0.05.Results: At 2 mm deflection, the maximum force values and unloading forces of Gummetalwere significantly higher than those of the control (SE-NiTi and Cu-NiTi) archwires. At 4 mm deflection, there was no significant difference between the maximum force values of Gummetal and SENiTiarchwires, however they were significantly higher than those of Cu-NiTiarchwire. Unloading forces of Gummetalarchwire at 4 mmdeflection were initially significantly higher, then became significantly lower than the control wires at 1 mm unloading deflection point.Conclusions: The present study showed that Gummetalarchwirewas less efficient in providing continuous forcesin comparison with SE-NiTi and Cu-NiTiarchwires.Gummetalarchwire cannot be considered superelastic, and its use in the alignment phase may better be limited to mild crowding cases.

Tensile Flow Behaviour and Fracture Studies of Beta Titanium Alloys at Elevated Temperatures

Tensile testing on metastable beta alloy with various microstructures was carried out in this study. Beta 21S is a metastable alloy that exhibits a wide range of material characteristics depending on the processing techniques used. Three different sheets that have been used in this paper which has the same substance but three different microstructures. At a strain rate of 0.001/s, the tensile test was done on a single sheet at five different temperatures. The sheet has developed varied microstructures, the tensile nature of the material varies the alloy’s characteristics. Mechanical characteristics for 400°C, 500°C, 600°C, and 7000°C are described for 21S sheets. The alpha phase sheet elongated at room temperature by 1-3 %, whereas the pure beta phase sheet elongated by 22-24 %. There is a significant improvement in the extension of the sheet with the variation in temperature for the alpha phase. The elongation of the pure beta phase does not alter as the temperature rises. The fracture surface was tested at all temperatures and the optimal temperature for forming the sheet has been determined

Causation of Oxidative Stress and Defense Response of a Yeast Cell Model after Treatment with Orthodontic Alloys Consisting of Metal Ions.

Misaligned teeth have a tremendous impact on oral and dental health, and the most efficient method of correcting the problem is orthodontic treatment with orthodontic appliances. The study was conducted to investigate the metal composition of selected orthodontic alloys, the release of metal ions, and the oxidative consequences that the metal ions may cause in the cell. Different sets of archwires, stainless steel brackets, and molar bands were incubated in artificial saliva for 90 days. The composition of each orthodontic material and quantification of the concentration of metal ions released were evaluated. Metal ion mixtures were prepared to determine the occurrence of oxidative stress, antioxidant enzyme defense system, and oxidative damage to proteins. The beta titanium alloy released the fewest metal ions and did not cause oxidative stress or protein damage. The metal ions from stainless steel and the cobalt-chromium alloy can cause oxidative stress and protein damage only at high concentrations. All metal ions from orthodontic alloys alter the activity of antioxidant enzymes in some way. The determined amounts of metal ions released from orthodontic appliances in a simulated oral environment are still below the maximum tolerated dose, and the concentrations of released metal ions are not capable of inducing oxidative stress, although some changes in antioxidant enzyme activity were observed at these concentrations.

Microstructure and wear behavior of inductive nitriding layer in Ti–25Nb–3Zr–2Sn–3Mo alloys

In human implant materials, beta (β) titanium alloys have been extensively used because of their excellent biocompatibility and lower elasticity modulus; however, they have poor hardness and wear resistance. Herein, vacuum induction nitriding technology is used to strengthen the surface of a Ti–25Nb–3Zr–2Sn–3Mo (TLM) alloy. The nitriding layer microstructure is characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM)–energy dispersive spectrometry (EDS) and optical microscopy (OM). The mechanical properties of nitriding layer are tested using cross-sectional hardness gradient and nano-indentation. Furthermore, the wear resistance and mechanism of nitriding layer are examined using a self-made reciprocating wear tester, a three-dimensional (3D) profilometer and SEM, respectively. The results demonstrate that an approximately 30-μm thick nitriding layer is formed on the TLM alloy surface after induction nitriding treatment. Interestingly, it forms a gradient structure that can improve the hardness and wear resistance of samples. Moreover, at a maximum test load of 10 N, the abrasion loss of the raw sample is 463 times that of the nitriding sample. Furthermore, the friction coefficient of the raw sample significantly exceeds that of the nitriding sample at three test loads. The wear mechanism between the friction pair Al 2 O 3 ball and the raw sample is primarily a combination of abrasive and adhesive wear, whereas that of the nitriding sample is primarily abrasive wear. The results demonstrate that the nitriding layer significantly improves the wear performance of TLM alloys. • The surface of TLM alloy can be rapidly strengthened by induction nitriding. • The gradient strengthening layer can be formed by induction nitriding. • The formation of gradient structure has excellent performance in improving the wear resistance of TLM alloy.

Effect of martensite on {332} twinning formation in a metastable beta titanium alloy

{332}β twinning and stress-induced martensite transformation are two important deformation mechanisms in the metastable beta titanium alloys, which can effectively strengthen the titanium alloys via twinning induced plasticity (TWIP) and transformation induced martensite (TRIP) effect, respectively. For a TWIP + TRIP metastable beta titanium alloy, {332}β twinning and stress-induced martensite can co-exist to improve the mechanical behaviors. However, the underlying mechanism for the co-existence of {332}β twinning and stress-induced martensite is not clear. Here we employed a model metastable beta titanium alloy Ti-2Al-9.2Mo-2Fe (wt%) to reveal the correlation between {332}β twinning and stress-induced martensite. The deformation gradient analysis and magnitude of shuffling needed for twining were utilized to reveal the relationship between {332} twinning and stress-induced martensite. As a result, we found that {332} twinning is a product of the reverse bcc to orthorhombic phase transformation. Such mechanism leads to a strong correlation between {332} twinning and stress-induced martensite, causing the {332} twinning combining stress-induced martensite in the present alloy.

Electrochemical and biological behaviour of near β Titanium alloy for biomedical implant applications

Pulsed laser deposition technique (PLD) is one of the methods to coat hydroxyapatite on near beta titanium alloys (Ti-13Nb-13Zr) implants which are used in orthopaedics and dentistry applications. In this study, Hydroxyapatite (HA) ceramics in the form of calcium phosphate (Cap) were deposited on nearβ Titanium alloys (Ti-13Nb-13Zr) by the pulsed laser deposition method. The coated thin film was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) with Energy dispersive spectroscopy (EDS) and atomic microscopy (AFM). The corrosion studies were carried out coated and uncoated samples using potentiodynamic polarisation studies in simulated body fluid (Hanks’ solution). The bioactivity of the Hap-coated samples on nearβ Titanium alloys was evaluated by immersing them in simulated body fluid (SBF) for nine days. XRD and EDS analysis confirmed the presence of hydroxyapatite. The corrosion studies showed that the treated samples have better corrosion resistance compared to uncoated substrates. The formation of apatite on treated samples revealed the bioactivity of the Hap-coated substrates. HA-coated nearβ Titanium alloys provide higher corrosion protection than substrates, which can be used for biomedical implant applications.

Cryogenic and Aging Treatment Effects on the Mechanical Properties of Ti-15V-3Al-3Cr-3Sn Titanium Alloy

Abstract In this study, single and duplex aging treatment was applied to the metastable beta titanium alloy of titanium-15 vanadium-3 aluminum-3 chromium-3 tin with cryogenic treatment. The single-step aging treatment was applied for 20 h at 450°C and 10 h at 550°C. The cryogenic treatment was carried out at −196°C for 24 h, followed by single-step or duplex aging treatment. The results obtained show that the cryogenic treatment causes the formation of martensitic alpha phases. Following the cryogenic treatment, martensitic alpha phases were observed in the sample, which was subjected to aging treatment at 450°C for 20 h, whereas these phases disappeared completely in the sample treated at 550°C for 10 h. Preaging treatment applied after cryogenic treatment prevented the formation of precipitate-free zones by providing a finer and uniform distribution of α phases. Cryogenic treatment followed by preaging treatment at 250°C for 24 h led to the formation of dense metastable prephases. This resulted in a 10% increase in tensile strength, 4% elongation, and 5% hardness compared to preaging at 300°C for 10 h after cryogenic treatment. The optimum mechanical properties in single-step sample groups were obtained in samples aged 20 h at 450°C. In duplex-aged samples, optimum mechanical properties were obtained in cryogenic treatment followed by 250°C/10 h + 450°C/20 h duplex aging treatment.